Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (736 page)

   Low-dose benzodiazepines may not be measurable by GC and HPLC (triazolam, flunitrazepam).

   GC/MS [MS].

   LC/MS/[MS].

   Target drug: parent drug and metabolites.

   Limit of quantitation: typically 5–20 ng/mL.

BETA-2 MICROGLOBULIN, SERUM, URINE, CEREBROSPINAL FLUID

   Definition

   β
₂
-Microglobulin is a cell membrane–associated 100-amino-acid peptide, a component of the lymphocyte HLA complex. Because it is present on all nucleated cells and is almost totally reabsorbed and catabolized by the proximal tubules, it serves as a marker of immune activation and proximal tubular function. It is found in nearly all body fluids.

   
Normal range:

   Serum: males: 0.60–2.28 mg/L; females: 0.60–2.45 mg/L

   Urine: 0–300 μg/L

   CSF: 1.5 + 0.2 mg/L

   Use

   Prognostic marker for some lymphoproliferative disorders (adult acute lymphocytic leukemia, AIDS).